Assembly for connecting a rotor to a helicopter

ABSTRACT

As assembly for connecting the lift rotor to a helicopter body filters out vibrations. In the assembly the rotor mast and associated elements form a self-supporting but resiliently deformable system.

United States Patent 1 1 1111 3,921,940

Mouille 1 Nov. 25, 1975 l l ASSEMBLY FOR CONNECTING A ROTOR [56]References Cited To A HELICOPTER UNITED STATES PATENTS [75] Inventor:Rene Louis Mouille, 2.615.657 10/1952 Young et 111. 244/1727Aix-en-Provence, France 2.739769 3/1956 Rogers 244/1727 3,502,290 3/1970Legrand et all. 244/1727 X Asslgnee: S0c1ete Natlonale lndustrlelleBulke ct 1 H 244/17 27 Aerospatiale, Paris. France 3.845.917 11 1974Drees 244/1727 [22] Filed: May 29, 1974 Primary E.\'aminerTrygve M. Blix[21] Appl' 474340 Assistant E.\'aminerPaul E. Sauberer Attorney, Agent,or Firml(arl W. Flocks [30] Foreign Application Priority Data June 8,1973 France 73.20960 [57] ABSTRACT As assembly for connecting the liftrotor to a helicop- [521 244/1727; 248/20; 248/358 R ter body filtersout vibrations. in the assembly the [51] Int. Cl. B64C 27/00 rotor mastand associated elements form a lf [58] Field of Search 244/1725. 17.27,17.11;

supporting but resiliently deformable system.

11 Claims, 12 Drawing Figures If M US. Patent Nov. 25, 1975 SheetlofS3,921,940

US. Patent Nov. 25, 1975 Sheet20f5 3,921,940

Sheet 3 of 5 US. Patent Nov. 25, 1975 US Patent Nov. 25, 1975 Sheet40f53,921,940

U.S. Patent Nov. 25, 1975 Sheet50f5 3,921,94fi

ASSEMBLY FOR CONNECTING A ROTOR TO A HELICOPTER This invention relatesto means for connecting the lift rotor of a helicopter to the fuselagethereof, the means being adapted to filter out or remove vibrationsbetween the rotor and the fuselage.

A main rotor of a helicopter has blades which transmit forces to the hubelements to which the blades are connected, some of such forces beingconstant and the others being intermittent. The constant forces are theaerodynamic lift and the resultant of the centrifugal forces and canreadily be dealt with by the structural elements of the helicopter.

The multiple intermittent or periodic forces mainly comprise verticalforces which arise because of the aerodynamic asymmetry caused by theflight speed and by forces acting in a plane perpendicular to the rotoraxis and caused by variations in blade drag. These alternating forcesare transmitted to the fuselage where they produce vertical andlongitudinal and more particularly transverse vibrations, the latterbeing the most disturbing both for the flight crew and for passengers.

Helicopter makers have endeavoured to reduce the effects of suchvibrations by providing the blades or hub with swinging resonators.Anti-vibration devices in the cabin which are tuned, automatically orotherwise, to the frequency to be neutralized have also been tried. Somepresent-day techniques reside in the provision of flexible connectionsbetween, on the one hand, the system embodied by the transmission box,mast and hub and, on the other hand, the helicopter structure.

With regard to vibration-reducing rotor suspension means, US. Pat. No.3,502,290 of Louis Francois Legrand and Charles Henri Tresch entitledVibration Danipin g Heli copter Rotor Support, issued Mar. 24,

1970, relates to a rotor-to-fuselage interconnection device comprisingrigid elements, such as rods disposed inclinedly between the top part ofthe casing of the main transmission box for transmitting the power ofthe rotor and the fuselage structure, the rigid elements being adaptedto take up the forces applied to the rotor head, and a cut plate forminga grille embodied by a number of strips, the plate working only in itsplane in response to the driving torque supplied by the maintransmission box and to the action of horizontal forces, to allow, bythe bending of the blades, slight alternating movements of the bottom ofthe transmission box relative to the fuselage.

A construction of this kind provides only incomplete removal ofvibrations between the rotor and the fuselage.

This invention relates to means for securing to a helicopter fuselagethe system embodied by the rotor, its mast and the reduction mechanism,the means helping to reduce the transmission of vibrations between therotor and fuselage.

According to the invention, the rotor mast and the elements rigidlysecured thereto form a rigid but resiliently deformable elongated systemballasted near its ends and having flexible intermediate portions, thesystem being adapted to vibrate transversely at a natural frequency veryslightly below the frequency to be removed, in a vibration mode causingvibration nodes to appear in the flexible portions, the connectingelements between such systems and the fuselage being disposed at suchnodes.

Preferably, the vibration regime is a two-node regime.

The system is connected to the helicopter fuselage at two places nearthe two vibration nodes, where movements are zero. The top-nodeconnection is in the form of a number of rigid inclined rods connectingthe top part of the reduction mechanism above the fuselage, the place onwhich such rods converge being disposed substantially at the node, thisconnection being adapted to transmit vertical and horizontal forces dueto bending movements of the suspended elements.

The bottom-node connection connects the bottom of the reductionmechanism to the fuselage structure by securing means adapted totransmit from the structure to the fuselage the driving torque andhorizontal forces due to bending moments of the suspended elements.

The invention as thus describedhas a number of considerable advantages.

More particularly, it is very light in weight since it mainly uses vitalparts of the helicopter, such as its transmission box, mast and rotor ascomponents of the vibrating unit whose vibration nodes are taken as thepositions for securing to the fuselage structure.

The invention can also be embodied to filter vibrations in one or moredirections.

In one form of the invention, size can be reduced by means of a lateralextension on either side of the transmission box which is combined witha flexible suspension of the bottom of such box.

With such a suspension, vibration problems can be dealt with muchearlier in the design of the machine and more simply than withconventional constructions since the system formed by the box, mast androtor can be optimized independently of the fuselage to provide anappropriate location of the nodes and therefore of the places forsecuring to the fuselage.

The remainder of the description now to be given, taken in conjunctionwith the accompanying drawings, will shown how the invention can becarried into effect. In the drawings:

FIG, 1 is a diagrammatic elevation of a helicopter having a suspensionsystem according to the invention;

FIG. 2 shows a construction which is effective in two directions;

FIG. 3 is a diagrammatic perspective view of a suspension systemaccording to the invention, the suspension being operativeuni-directionally;

FIG. 4 is a diagrammatic perspective view of a rotor system having aunidirectional suspension combined with a resilient box bottomsuspension;

FIG. 5 shows a variant of the two-directional suspension of reducedoverall height;

FIG. 6 shows a constructional variant of the device of FIG. 3;

FIGS. 7, 8 and 9 are diagrammatic views showing the behaviour of thevariant of FIG. 6;

FIGS. 10 and 11 show details of the forms of securing of the systemshown in FIG. 6; and

FIG. 12 is an elevation of a light helicopter having an anti-vibrationsuspension according to the invention,

Referring to FIG. 1, a helicopter fuselage l carries at the top a systemembodied by a main transmission box 2 topped by a mast 3 forming a shaftfor a lift rotor 4 disposed at the top end of mast 3.' driving unit Mdrives rotor 4 via box 2, the connectihgshaft between the integers M and2 having provisiotr'to enable them to make reduced longitudinal andvertical out-ofalignment movements.

The rotor forms one ballast; a second ballast, 5,-in the form of aweight disposed opposite the first ballast and on the same vertical axisis secured to the bottom of box 2 by wayof a flexible mast a. The twoballasts 4, 5 at the. ends of the masts 3 and 5a and of the box 2 form arigid resilient system which can vibrate and produce a deformed shape6a, 6b having two nodes 7, 8. The connections to the fuselage structureare disposed at the nodes 7, 8.

Accordingly, four rods, as 9, which are articulated at their. ends takeup the forces applied to the rotor head and, byway of pivot points 10,connect the fuselage structure to the top part of the casing 2 at pivotpoints 11 disposed substantially in the plane of the top node 7. At thebottom node 8 the fuselage l is connected to the vertical system formedby the box and the mast. for instance, by means of a universal jointl2or of a flector adapted to transmit the rotor torque, as shown in theperspective view in FIG. 2.

As a rule. and more particularly in the case of exist-- ing craft, therequired space is not available below the box, since such base isusually fully taken up in a helicopter. The construction shown in FIG. 3obviates such a disadvantage, As in the previous case, rotor 4 forms thefirst ballast; the second additional ballast is split and secured to across-beam 13 having an annular widening 14 so that is can be rigidlysecured to the underside of transmission box casing 2. The two arms 15.beam 13 extend laterally frompart 14 on either side of the fuselagelongitudinal axis 17 and carrya weight 18 at each of their ends.

The nodes of the distorted shape caused by longitudinal vibrations.represented by arrows 19, are disposed at a place 20, on which the rods9 converge, and at places 21, 22 where the beam 13 is secured to thestructure. The latter beam securing places are in the form' of flexibleconnections such as flexible bearings which operate in compression andwhich can make reduced lateral movements.

A ballasted cross-beam of this kind which is secured to the bottom oftransmission box 2 also enables the beam to operate as a resonatoradapted to withstand purely vertical vibrations coming from the rotor;however, vertical vibrations are the least disturbing.

Referring to the variant of FIG. 4, rotor mast 3 bearing the rotor 4forming the top ballast experiences not only longitudinal vibrations 19but also lateral vibrations '23. The longitudinal vibrations 19 aretaken up by cross-beam 13, which has its ends ballasted, and the lateralvibrations 23 are filtered at the distortion nodes 21, 22 of beam 13 bymeans of resilient abutments 24, such as abutments made of clastomericlaminations. The abutments 24 are disposed substantially at the nodes21, 22 so as to withstand the rotor torque, being connected to the beamarms 15, I6 and, for instance by way of angle-members, as 25, to thefuselage structure.

In the embodiment shown in FIG. 5, the bottom of the transmission boxhas the beam 13 of FIG. 3, but the beam is not directly connected to thestructure and the two nodes 21, 22, an intermediate beam 26 beinginterposed between the elongated vibrating rigid assembly and thefuselage structure. Beam 26 comprises aflat circular disc 27 which isconnected to the positions 2], 22 of beam 13 and which hasarms 28, 29disposed in the direction of the helicopter longitudinal axis. Each arm28, 29 {carries atits end a weight 30, the system formed by the ring 27and the arms 28, 29 forming the beam 26. When the top of the rotorexperiences longitudinal and transverse vibrations, the disc 27 distortsin its plane. the distortion having two nodes 31, 32 which are used forthe connection to the structure.

Referring to FIG. 6, casing 2 has a single cross-beam 33 which issecured to the bottom of easing 2 and which carries a weight 34 at eachend.

Beam-33 has vertical inertia and longitudinalinertia such that thedistortion pattern is of the two-node kind with a double bottom node 35,36, the position of the bottom node being the same for longitudinal andfor transverse vibrations, for since inertia weights and identicallengths are involved, the two nodes 35, 36 are in duplicate and aredisposed at the same positions for both kinds of vibration.

FIG. 7 shows two-node type distortion caused by longitudinal vibrationswith beating of the weights 34 in the horizontal plane.

FIG. 8 shows two-node type distortion due to lateral vibrations, withbeating of the weights 34 in a vertical plane and a slight alternatelateral shifting of the two nodes35, 36. The total shift of the nodes isindicated by reference A.

In this case of just a single ballasted cross-beam providing both kindsof vibration, provision must be made for the beam to shift laterally. Tothis end, the nodes can be connected to the structure (at places 35 and36) by way of a plain bearing 37 (visible in FIGS. 6, l0 and 11) withresilient restoration, for instance, a bearing made of an elastomerwhich may or may not be laminated. Each node can also be connected tothe structure by means of two rods 38 which are shown in FIG. 9 andwhich are swivel mounted at their ends on beam 33 and on the structure.and which are associated with a resilient transverse restoring or returnelement 38a which provides transverse location of the system whileallowing it some freedom of transverse movement. The rods 38 areadaptedto withstand the rotor reaction torque.

Referring to the helicopter shown in FIG. 12, the system embodied bymotor 39, reducer casing 40, rotor mast 41 and rotor hub 42 is used toform a vibrating system whose vibration mode, with its two nodes 43, 44corresponds to approximately 0.8 times the frequency which it isrequired to neutralize.

To locate the node 44 disposed between motor 39 and reducer 40, suchmotor and such reducer are interconnected by a rigid element adapted forflexible bending. The second node is disposed above the reducer 40 at aplace 43 whose position depends upon the length and rigidity of mast 41and upon the weight of rotor 42.

The mounting points of the vibrating system are located at the two nodes43, 44.

The torque arising from the reducer is taken up at the bottom node 44,and the means providing a connection with fuselage structure 45 can be auniversal joint or a flector or an ordinary flange connection, in whichevent the flange itself or the mechanical floor 46 of the craft acts asa flexible diaphragm.

The forces applied to the top of the rotor are taken up by a system ofrigid rods 47 which connect the structure by way of pivot points 48 andthe top node 43 t0 the vibrating system.

The invention is of use for all aircraft which have at least one mainrotor producing vibrations.

I claim:

1. An assembly for securing a main rotor of a helicopter to the fuselagetherof, the assembly being adapted to prevent vibrations from beingtransmitted from the rotor to the fuselage, wherein the rotor mast andthe elements rigidly secured thereto form a rigid but resilientlydeformable, vertically elongated system ballasted near its upper andlower ends and having at least one flexible vertically elongatedintermediate portion, the system being adapted to vibrate in a vibrationmode causing vibration nodes to appear in vertically spaced parts of theflexible vertically elongated portion, the connecting elements betweensuch system and the fuselage being disposed at such vertically spacednodes.

2. An assembly for securing a main rotor of a helicopter to the fuselagethereof, the assembly being adapted to prevent vibrations from beingtransmitted from the rotor to the fuselage wherein the rotor mast andthe elements rigidly secured thereto form a rigid but resilientlydeformable elongated system ballasted near its ends and having flexibleintermediate portions, the system being adapted to vibrate transverselyat a natural frequency very slightly below the frequency to be removed,in a vibration mode causing vibration nodes to appear in the flexibleportions, the connecting elements between such system and the fuselagebeing disposed at such nodes, said elongated system connected to thefuselage at the top node nearest the rotor by way of a rigid securingadapted to transmit horizontal and vertical forces and at the bottomnode by way of a flexible device adapted to transfer to the fuselage thedriving torque applied to the elongated system and to transmithorizontal forces with the possibility of slight lateral movements.

3. An assembly for securing a main rotor of a helicopter to the fuselagethereof, the assembly being adapted to prevent vibrations from beingtransmitted from the rotor to the fuselage wherein the rotor mast andthe elements rigidly secured thereto form a rigid but resilientlydeformable elongated system ballasted near its ends and having flexibleintermediate portions, the system being adapted to vibrate transverselyat a natural frequency very slightly below the frequency to be removed,in a vibration mode causing vibration nodes to appear in the flexibleportions, the connecting elements between such system and the fuselagebeing disposed at such nodes, said elongated system substantiallystraight and vertical and, with the rotor forming the ballast at the topend, the main transmission box forming a central weight, a ballastdisposed at the bottom end, the intermediate flexible portions beingcomprised between such box and each of the two ballasts.

4. An assembly according to claim 3, wherein the bottom ballast is anextra weight.

5. An assembly according to claim 3 wherein the bottom ballast is therotor-driving motor.

6. An assembly for securing a main rotor of a helicopter to the fuselagethereof, the assembly being adapted to prevent vibrations from beingtransmitted from the rotor to the fuselage wherein the rotor mast andthe elements rigidly secured thereto form a rigid but resilientlydeformable elongated system ballasted near its ends and having flexibleintermediate portions, the system being adapted to vibrate transverselyat a natural frequency very slightly below the frequency to be removed,in a vibration mode causing vibration nodes to appear in the flexibleportions, the connecting elements between such system and the fuselagebeing disposed at such nodes, said elongated system comprising avertical straight portion comprising the main transmission box and therotor separated by an intermediate flexible portion, and a portion whichis transverse to the first portion and which is rigidly secured to thebase thereof and which comprises flexible portions terminating inballasts.

7. An assembly according to claim 6 wherein the transverse portion isperpendicular to fuselage length and forms an inverted T with the firstportion.

8. An assembly according to claim 7, wherein the stroke of the invertedT is disposed along the fuselage longitudinal axis.

9. An assembly according to claim 7, wherein the means connecting theflexible portions of the transverse part are resilient securingpositions.

10. An assembly according to claim 7, wherein the elements forconnecting the flexible portions of the transverse part allow transverseshifting of such portions.

11. An assembly according to claim 6, wherein the transverse partcomprises a flrst portion perpendicular to fuselage length and formingan inverted T with the first part, and a second portion which extends inthe direction of fuselage length and which is assembled resiliently tothe first part near each of its two flexible portions, such secondportion being connected to the fuse-

1. An assembly for securing a main rotor of a helicopter to the fuselagetherof, the assembly being adapted to prevent vibrations from beingtransmitted from the rotor to the fuselage, wherein the rotor mast andthe elements rigidly secured thereto form a rigid but resilientlydeformable, vertically elongated system ballasted near its upper andlower ends and having at least one flexible vertically elongatedintermediate portion, the system being adapted to vibrate in a vibrationmode causing vibration nodes to appear in vertically spaced parts of theflexible vertically elongated portion, the connecting elements betweensuch system and the fuselage being disposed at such vertically spacednodes.
 2. An assembly for securing a main rotor of a helicopter to thefuselage thereof, the assembly being adapted to prevent vibrations frombeing transmitted from the rotor to the fuselage wherein the rotor mastand the elements rigidly secured thereto form a rigid but resilientlydeformable elongated system ballasted near its ends and having flexibleintermediate portions, the system being adapted to vibrate transverselyat a natural frequency very slightly below the frequency to be removed,in a vibration mode causing vibration nodes to appear in the flexibleportions, the connecting elements between such system and the fuselagebeing disposed at such nodes, said elongated system connected to thefuselage at the top node nearest the rotor by way of a rigid securingadapted to transmit horizontal and vertical forces and at the bottomnode by way of a flexible device adapted to tRansfer to the fuselage thedriving torque applied to the elongated system and to transmithorizontal forces with the possibility of slight lateral movements. 3.An assembly for securing a main rotor of a helicopter to the fuselagethereof, the assembly being adapted to prevent vibrations from beingtransmitted from the rotor to the fuselage wherein the rotor mast andthe elements rigidly secured thereto form a rigid but resilientlydeformable elongated system ballasted near its ends and having flexibleintermediate portions, the system being adapted to vibrate transverselyat a natural frequency very slightly below the frequency to be removed,in a vibration mode causing vibration nodes to appear in the flexibleportions, the connecting elements between such system and the fuselagebeing disposed at such nodes, said elongated system substantiallystraight and vertical and, with the rotor forming the ballast at the topend, the main transmission box forming a central weight, a ballastdisposed at the bottom end, the intermediate flexible portions beingcomprised between such box and each of the two ballasts.
 4. An assemblyaccording to claim 3, wherein the bottom ballast is an extra weight. 5.An assembly according to claim 3 wherein the bottom ballast is therotor-driving motor.
 6. An assembly for securing a main rotor of ahelicopter to the fuselage thereof, the assembly being adapted toprevent vibrations from being transmitted from the rotor to the fuselagewherein the rotor mast and the elements rigidly secured thereto form arigid but resiliently deformable elongated system ballasted near itsends and having flexible intermediate portions, the system being adaptedto vibrate transversely at a natural frequency very slightly below thefrequency to be removed, in a vibration mode causing vibration nodes toappear in the flexible portions, the connecting elements between suchsystem and the fuselage being disposed at such nodes, said elongatedsystem comprising a vertical straight portion comprising the maintransmission box and the rotor separated by an intermediate flexibleportion, and a portion which is transverse to the first portion andwhich is rigidly secured to the base thereof and which comprisesflexible portions terminating in ballasts.
 7. An assembly according toclaim 6 wherein the transverse portion is perpendicular to fuselagelength and forms an inverted T with the first portion.
 8. An assemblyaccording to claim 7, wherein the stroke of the inverted T is disposedalong the fuselage longitudinal axis.
 9. An assembly according to claim7, wherein the means connecting the flexible portions of the transversepart are resilient securing positions.
 10. An assembly according toclaim 7, wherein the elements for connecting the flexible portions ofthe transverse part allow transverse shifting of such portions.
 11. Anassembly according to claim 6, wherein the transverse part comprises afirst portion perpendicular to fuselage length and forming an inverted Twith the first part, and a second portion which extends in the directionof fuselage length and which is assembled resiliently to the first partnear each of its two flexible portions, such second portion beingconnected to the fuselage by its own flexible portions.